1. Field of the Invention
This invention generally relates to portable electronic devices and, more particularly, to a system and method for protecting multiplexed elements sharing a single electrical line.
2. Description of the Related Art
FIG. 6 is a schematic block diagram depicting a plurality of elements multiplexed on a single line in a wireless communications device (prior art). A wireless telephone device is used as an example in the following discussion, however, it should be understood that the discussion applies to other electrical devices multiplexing elements on a single line. Wireless device users demand smaller devices with added capabilities, creating in turn, a need to reduce the number of components in the device. As shown in FIG. 6, it is known to multiplex multiple elements on a single line to reduce the number of components in a device. For example, if elements that interface with devices external to the wireless device, for example, a headset, share a single line and a single interface port, the component count for the device can be reduced by eliminating the need to use separate interface ports for individual elements or sub-groupings of elements.
Unfortunately, there are limitations associated with the multiplexing scheme noted above. Among the limitations is the compatibility, particularly the voltage compatibility, of elements sharing a single line. Elements in a wireless device have different operating voltages and different thresholds of destruction (typically a function of element geometry). Physically linking elements with sufficiently different thresholds of destruction can result in damage to elements with lower thresholds. Therefore, the configuration shown in FIG. 6 is restricted to certain combinations of elements. For example, in FIG. 6, assume element A is an audio amplifier and element B supplies or accepts a DC signal of between 4.5 and 5.5V. If these two elements are multiplexed on the same line, element A can be back driven with a DC voltage from element B exceeding its threshold of destruction. Thus, elements A and B cannot be multiplexed on the same line and separate electrical interface ports are required to accommodate elements A and B. Unfortunately, failing to limit the number of parts, such as electrical interface ports, in a device can limit the size to which the wireless device can be reduced and can limit space available for other components. Increasing the parts count for a wireless device also adds to the cost of producing the wireless device.
It would be advantageous if elements with incompatible thresholds of destruction could be multiplexed on the same electrical line.
It would be advantageous if elements multiplexed on a single electrical line could be protected from voltage incompatibilities.